Multifocal diffractive ophthalmic lens using suppressed diffractive order

ABSTRACT

A multifocal ophthalmic lens includes an ophthalmic lens and a diffractive element. The ophthalmic lens has a base curvature corresponding to a base power. The diffractive element produces constructive interference in at least four consecutive diffractive orders corresponding a range of vision between near and distance vision. The constructive interference produces a near focus, a distance focus corresponding to the base power of the ophthalmic lens, and an intermediate focus between the near focus and the distance focus. A diffraction efficiency of at least one of the diffractive orders is suppressed to less than ten percent.

TECHNICAL FIELD

The present invention relates generally to multifocal ophthalmic lensesand more specifically to a multifocal diffractive ophthalmic lens with asuppressed diffractive order.

BACKGROUND

The human eye functions to provide vision by refracting light through aclear outer portion called the cornea, and refracting the light by wayof a crystalline lens onto a retina. The quality of the focused imagedepends on many factors including the size and shape of the eye, and thetransparency of the cornea and the lens. When age or disease causes thelens to become aberrated, vision deteriorates because of the loss ofretinal image quality. This loss of optical quality in the lens of theeye is medically known as a cataract. An accepted treatment for thiscondition is surgical removal of the lens and replacement of the lensfunction by an artificial intraocular lens (IOL). As the eye ages, itmay also lose the ability to change focus to nearer focal points, knownas accommodation. This loss of accommodation with age is known aspresbyopia.

In the United States, the majority of cataractous lenses are removed bya surgical technique called phacoemulsification. During this procedure,a portion of the anterior capsule is removed and a thinphacoemulsification cutting tip is inserted into the diseased lens andvibrated ultrasonically. The vibrating cutting tip liquefies oremulsifies the nucleus and cortex of the lens so that the lens may beaspirated out of the eye. The diseased nucleus and cortex of the lens,once removed, is replaced by an artificial intraocular lens (IOL) in theremaining capsule (in-the-bag). In order to at least partially restorethe patient's ability to see in focus at near distances, the implantedIOL may be a multifocal lens.

One common type of multifocal lens is a diffractive lens, such as abifocal lens providing distance vision and near (or intermediate)vision. Trifocal diffractive lenses are also available that provide anadditional focal point and, at least potentially, a broader range ofin-focus vision. However, there are disadvantages associated withdividing light energy among multiple focal points, particularly intrifocal lenses. Thus, there remains a need for improved multifocaldiffractive lenses.

SUMMARY

In various embodiments of the invention, a multifocal ophthalmic lensincludes an ophthalmic lens and a diffractive element. The ophthalmiclens has a base curvature corresponding to a base power. The diffractiveelement produces constructive interference in at least four consecutivediffractive orders corresponding a range of vision between near anddistance vision. The constructive interference produces a near focus, adistance focus corresponding to the base power of the ophthalmic lens,and an intermediate focus between the near focus and the distance focus.A diffraction efficiency of at least one of the diffractive orders issuppressed to less than ten percent.

Other features and advantages of various embodiments of the presentinvention will be apparent to one skilled in the art from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an intraocular lens according to particularembodiments of the present invention;

FIG. 2 illustrates a diffractive step arrangement according toparticular embodiments of the present invention; and

FIGS. 3-8 are tables illustrating particular diffractive steparrangements according to particular embodiments of the presentinvention.

DETAILED DESCRIPTION

Various embodiments of the present invention provide a multifocaldiffractive ophthalmic lens with at least one suppressed diffractiveorder. By suppression of one diffractive order, the performance of thelens can be tailored relative to conventional diffractive lenses. Knowntrifocal diffractive lenses, for example, divide light between multiplediffractive foci, such as (−1, 0, +1) order foci or (0, +1, +2) orderfoci.

By contrast, various embodiments of the present invention provide atleast three foci corresponding to diffractive orders wherein at leastone intermediate diffractive order is suppressed. This provides anintermediate focus that is closer either to distance vision or nearvision, which provides a broader range of vision around the respectivefocus. Furthermore, suppression of the other intermediate orderdistributes more energy to the other foci, which may provide more usefulvision. In the following description, the references to foci for anophthalmic lens refer to a corresponding diffractive focus within therange of vision extending from ordinary near viewing around 30 cm todistance vision (essentially modeled as collinear light rays frominfinite distance). This excludes spurious higher orders of diffractivelenses that lie outside the range of vision, which provide only unwantedlight effects. Thus, for example, even diffractive lenses that arenominally bifocal include higher-order diffractive foci fromconstructive interference, but for purposes of this specification, thoseshould not be considered foci of the ophthalmic lens.

In other embodiments, a multifocal diffactive lens produces focicorresponding to at least four consecutive diffractive orders includingat least one focus less than one half of the near-most add power and atleast one other focus greater than one half of the nearmost add power.This may be advantageous over conventional trifocal lenses, which havean add power that is half of the nearmost add power. This intermediatevision corresponds to twice the near-vision distance, so that if thenear add-power corresponds to a working distance of 40 cm, aconventional reading distance, the intermediate viewing distance wouldbe 80 cm. Given that a common intermediate working distance is at 60 cm,this would not provide a sharp focus at the most common workingdistance, which would fall between the near and intermediate foci. Bycontrast, a lens with a focus corresponding to ⅔ of the near add powerwould provide a focus at 60 cm, corresponding to the intermediateworking distance.

FIG. 1 illustrates a particular embodiment of a multifocal diffractiveophthalmic lens (IOL) 100 including a diffractive element 102. Thediffractive element 102 comprises diffractive steps 104 (also known aszones) having a characteristic radial separation to produce constructiveinterference at characteristic foci. In principle, any diffractiveelement that produces constructive interference through phase shiftingin interfering zones, often referred to as a hologram, can be adaptedfor use in such a multifocal diffractive ophthalmic lens. Also, whilethe diffractive element is depicted with annular zones, the zones couldconceivably be partial, such as semicircular or sectored zones, as well.While the following description will concern a diffractive element 102including annular diffractive steps 103, it should be understood bythose skilled in the art that suitable substitutions may be made in anyembodiment discloses herein.

IOL 100 also includes an optic 104 on which the diffractive element 102is located. The optic 104 determines the base optical power of the lens,which typically corresponds to the distance vision of the patient. Thisneed not always the case; for example, a non-dominant eye may have anIOL with a base optical power is slightly less than the correspondingdistance power for the patient to improve overall binocular vision forboth eyes. Regardless, the add power for the IOL can be defined withrespect to the base optical power. Haptics 106 hold the IOL 100 inplace, providing stable fixation within the capsular bag. Althoughhaptic arms are illustrated in the example, any suitable hapticsfixation structure for the capsular bag or the ciliary sulcus compatiblewith posterior chamber implantation could also be used in a posteriorchamber IOL.

Although the example below deals with a posterior chamber IOL 100, otherophthalmic lenses, including multifocal diffractive spectacles andmultifocal diffractive contact lenses, could also benefit from the sameapproach. The known and fixed position of the lens relative to theoptical axis makes such applications particularly advantageous forintraocular lenses, including intracorneal, anterior chamber, andposterior chamber lenses. However, this does not exclude the utility ofmultifocality in other applications.

FIG. 2 illustrates, in more detail, a diffractive step structure usefulfor ophthalmic lenses such as the IOL 100 of FIG. 1. In particular, FIG.2 illustrates a three-step repeating diffractive structure that producesa phase relationship for constructive interference at four differentfocal points within the range of vision. The step relationship atconsecutive radial step boundaries along a scaled radial axis (x-axis),measured in r²-space, is as follows:

$y_{i} = {{\frac{A_{i}}{x_{i} - x_{i - 1}}\left( {x - x_{i - 1}} \right)} + {\varphi_{i}\mspace{11mu} \left( {{i = 1},2,3} \right)}}$

wherein A_(i) is the corresponding step height relative to the basecurvature (base optical power) of the base lens (excluding the constantphase delay φ_(i)), y_(i) is the sag in the corresponding segment(height above or below the x-axis), φ_(i) is the relative phase delayfrom the x-axis, and x_(i) is the position of the step along the x-axis.As will be apparent to one skilled in the art of diffractive optics, theradial position indicated in the formula is in r²-space (i.e.,parabolically scaled), as expected for zone spacing. In particularembodiments, the parameters are selected so that one of the foci issuppressed, which is to say that the light energy is reduced relative tothe division among the foci such that the focused image is no longervisibly perceptible. This corresponds to a light energy of less than 10%of the incident light energy, as suggested by the fact that bifocallenses with spurious diffractive orders of less than 10% of incidentlight energy do not result in separately perceptible images. Thefraction of incident light energy focused at a particular order isreferred to as the “diffraction efficiency.”

The listed phase relationships are given with respect to the base curvedetermined by the base power of the IOL, corresponding to the zero-orderdiffractive focus for the lens. The radial spacing of the zones x_(i) isordinarily determined based on the ordinary Fresnel zone spacing inr²-space as determined by the diffractive add power, although it can bevaried to adjust the relative phase relationship between the componentsin ways known in the art to slightly modify the energy distributionbetween the foci. In the examples listed below, the spacing should beassumed to according to the known Fresnel pattern for producing fourfoci. This is analogous to the trifocal approach described in, e.g.,U.S. Pat. Nos. 5,344,447 and 5,760,817 and PCT publication WO2010/0093975, all of which are incorporated by reference. Thediffractive steps can also be apodized (gradually reduced in step heightrelative to the nominal phase relationship) to reduce glare byprogressively reducing the energy to the near focus in the mannerdescribed in U.S. Pat. No. 5,699,142.

FIGS. 3-8 provide example multifocal embodiments for a (0, +1, +2, +3)diffractive lens wherein the +1 order is suppressed. This advantageouslyprovides an intermediate focus at ⅔ of the near add power, correspondingrespectively to a focused image at 60 cm and 40 cm distance. Notably,the diffraction efficiency for the distance vision (zero-order) focuscan be nearly 40%, comparable to the diffraction efficiency forconventional bifocal lenses, and the diffraction efficiency for thesuppressed first-order focus can be less than 5%, while still providingvisible intermediate and near foci at normal working distances of 60 cmand 40 cm, respectively. Compared to conventional multifocals, thisbetter approximates the full range of working vision that a patientwould use in the absence of the presbyopic condition.

Although particular embodiments have been described herein, one skilledin the art will appreciate that numerous variations are possible. Inparticular, the embodiments described herein are multifocal posteriorchamber IOLs using (0, +1, +2, +3) diffractive orders with the +1 orderbeing suppressed. This four-order embodiment could use differentconsecutive diffractive orders, such as starting with an order from −4to −1, for example. And while it is desirable for the zero-order to beincluded for distance vision, that condition is not a necessaryconstraint. Lastly, the approach could be applied in principle to morethan four diffractive orders; for example, a five-order diffractive lenscould have add powers including two intermediate powers, a near power,and a suppressed intermediate power.

What is claimed is:
 1. An intraocular lens, comprising: an ophthalmiclens having a base curvature corresponding to a base power; and adiffractive profile disposed on at least one of the anterior surface andthe posterior surface, the diffractive profile comprising a plurality ofannular zones configured to produce constructive interference in atleast four consecutive diffractive orders corresponding a range ofvision; wherein: the constructive interference produces a near focus, adistance focus corresponding to the base power of the intraocular lens,and an intermediate focus, each corresponding to a different one of thefour consecutive diffractive orders; and a lowest diffractive order ofthe consecutive diffractive orders corresponds to the distance focus;and a diffraction efficiency of the lowest diffractive order is greaterthan a diffraction efficiency of any other of the consecutivediffractive orders.
 2. The intraocular lens of claim 1, wherein adiffraction efficiency of at least one of the diffractive orders issuppressed to less than ten percent.
 3. The intraocular lens of claim 2,wherein at least a portion of the energy associated with the suppresseddiffractive order is redistributed to one or more of the near focus, theintermediate focus, and the distance focus.
 4. The intraocular lens ofclaim 1, wherein the four consecutive diffractive orders include alowest diffractive order, a highest diffractive order, and twointermediate diffractive orders; and the at least one suppresseddiffractive order is one of the two intermediate diffractive orders. 5.The intraocular lens of claim 1, wherein the four consecutivediffractive orders include at least two of the following diffractiveorders: −4, −3, −2, −1, 0, +1, +2 and +3.
 6. The intraocular lens ofclaim 1, wherein the distance focus corresponds to a 0th diffractiveorder.
 7. The intraocular lens of claim 1, wherein the distance focuscorresponds to a diffractive order other than the 0^(th) order.
 8. Theintraocular lens of claim 1, wherein the three-zone diffractivestructure includes repeating sets of diffractive steps.
 9. Theintraocular lens of claim 1, wherein the near focus corresponds tovision at 40 cm, and the intermediate focus corresponds to vision at 60cm.
 10. An intraocular lens, comprising: an ophthalmic lens having abase curvature corresponding to a base power; and a diffractive profiledisposed on at least one of the anterior surface and the posteriorsurface, the diffractive profile comprising a plurality of annular zonesconfigured to produce constructive interference in at least fourconsecutive diffractive orders corresponding a range of vision; wherein:the constructive interference produces a near focus, a distance focuscorresponding to the base power of the intraocular lens, anear-intermediate focus, and a far-intermediate focus, eachcorresponding to a different one of the four consecutive diffractiveorders; the near focus, the near-intermediate focus, and thefar-intermediate focus each correspond to a different add power relativeto a the base power; a first add power corresponding to thefar-intermediate focus is less than one half of a third add powercorresponding to the near focus; and a second add power corresponding tothe near-intermediate focus is greater than one half of the third addpower corresponding to the near focus.
 11. The intraocular lens of claim10, wherein the four consecutive diffractive orders include a lowestdiffractive order, a highest diffractive order, and two intermediatediffractive orders; and at least one of the consecutive diffractiveorders is suppressed.
 12. The intraocular lens of claim 11, wherein thefour consecutive diffractive orders include a lowest diffractive order,a highest diffractive order, and two intermediate diffractive orders;and the at least one suppressed diffractive order is one of the twointermediate diffractive orders.
 13. The intraocular lens of claim 12,wherein at least a portion of energy associated with the at least onesuppressed diffractive order is redistributed to one or more of the nearfocus, the intermediate focus, and the distance focus.
 14. Theintraocular lens of claim 10, wherein the four consecutive diffractiveorders include a lowest diffractive order, a highest diffractive order,and two intermediate diffractive orders; and a diffraction efficiency ofthe lowest diffractive order is greater than a diffraction efficiency ofany other of the consecutive diffractive orders.
 15. The intraocularlens of claim 10, wherein the four consecutive diffractive ordersinclude at least two of the following diffractive orders: −4, −3, −2,−1, 0, +1, +2 and +3.
 16. The intraocular lens of claim 10, wherein thedistance focus corresponds to a 0th diffractive order.
 17. Theintraocular lens of claim 10, wherein the distance focus corresponds toa diffractive order other than the 0^(th) order.
 18. The intraocularlens of claim 10, wherein the plurality of annular zones comprises aplurality of repeating diffractive steps.